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[Ridgekid]

Still tweaking on my Grunfos. I've learned the following:

On my system:
@ 2 gpm I get a 30* drop across my exchanger
@ 3 gpm I get  a 25* drop across my exchanger
@  4 gpm I get a 20* drop across my exchanger

Do you look for a minimum gpm or a certain temp drop across an exchanger?

[artbaldoni]

Wondering the same thing in a low tech way. What circ speed is the best? Still have the original 3 speed circ on my NC.

[MTJAG]

As with anything with multiple variables, there is a sweet spot.  Since we can't control all the variables, we can control certain variables such as return water speed, setpoints on our boilers and furnaces.  Somewhere in this is an optimal performance...maybe

I've got another question to add to this...does anyone try to insulate their heat exchangers?  I have two 50 plate exchangers that put off alot of heat in my basement.

[willieG]

i guess you need to know a couple of things..first  how did you size the exchanger for your home heating..you should know how many btu per hour you need to heat your home, now it is said that 180 degree water will deliver 10,000 btu per hour to your home per GPM so if you think on the coldest day of the year you will need 60,000 btu per hour then you should have an exchanger that can pull that much from your water and you should be able to deliver at least 6 pgm to attain that many btu

your blower speed will also have an impact on how many btu you pull from your exchanger (i am not sure how to figure that out)

i have an "inground water furnace' that has a 2  speed blower, it  runs in low speed 24/7 and since i installed my OWB it has never had to kick into high speed. i have large ductwork because the water furnace needs to move a lot of air as it does not make very hot air when and if it ever runs. i have enough heat exchangers in the plenum  for 140,000 btu but i know i never draw that much with the fan in low. my water comes to the house at 160 or so and with just the furnace drawing heat it leaves at about 150, if the house is calling for heat and the doemestic water is also running the return will drop another 10

i have seen my stoves temp on a cold night and when using doemestic water and the furnace  drop the temp of the OWB 5 to 7 degrees below the "blower on" temp before the OWB starts to catch up

as for sweet spot..i have no idea. i tend to lean towards that most indoor boilers say to keep your return no more than 20 degrees cooler than your delivery so i think that may be a target for us as well?

i think (not 100 percent certain) my pump is delivering  about 5 or 6 gpm

i guess i would say ..oversize your exchanger (most do anyway as you should fill yoru plenum  to prevent cool air from going around it)

pump enough water to keep near the 20 degree differential between feed and return.

just my thoughts..im sure others do differently

[Ridgekid]

The heat exchanger for furnace is 100k btu. The air handler is a trane. Not sure what the flow rate is. Here's the model number. twe036c140a0

I found it.  It's 1500 cfm!!!!!

Sorry. That other number was the cfm of the outdoor unit fan. 

[Scott7m]

I'm not sure if there is a magic number, 20 degrees sounds good.  But as far as there being an exact number that I'm not sure!

[Scott7m]

I replied in your pump thread on some thoughts I had.

[Ridgekid]

Thanks Scott. I too replied to your added comments.

[RSI]

The biggest thing is getting enough heat in the house. How much difference is the temperature of the DHW coming out of the plate heat exchanger?

Another thing is how good it is mixing the water in the boiler. It might be cold at the bottom and hot at the top. It probably isn't an issue on your boiler because most CB's hold quite a bit of water but low flow rate could cause boil over on some stoves.
If the real low circulating rate is causing dead circulation areas it may rust through faster. You might want to check with CB and see if they have a minimum recommended flow rate.I would guess your old pump was running around 8gpm or so.

[fireboss]

i wrap my ex with insulation . Iam loseind 30* on the coldest nights between my boiler and the ex .Iam running 007 on both sides not sure why?

[Ridgekid]

RSI -  again you bring very good points to light. You are right about the return line and the controller sensing point.  I have noticed it overshoots on burns about 1-2* with the lower flow rate. I need to look into this unless someone knows the minimum flow for a cb classic?

Fireboss- this discussion is about heat load across a heat exchanger. To confirm, your losing 30* before the heat exchanger? Sounds like a underground pex issue. Many discussion already started on it.

[johnybcold]

30 seems like alot of lost heat, my return at the own is about 10 less then the temp going out I have a 140' run

[donahuej]

MTJag,

I say insulate the heck out of everything. My 50 plate is wrapped in duck insulation and then I stuffed fiberglass all around it, it's in my crawl space.  My line set in the house I used the 1" fiberglass insulation. from Mansfield, the boiler line kind.  All that hard work I put into the systems and the firewood - I want the heat to go where I need it to go - DHW and my water to air heat exchangers in my plenums.

[Scott7m]

Let's clarify this...   He's just measuring from the intake side of his hx to the return side.  Not from the stove.  He loses The same number of btu but the variable is the water flow, faster water loses less heat but you have to move more of it.  He's running his pump 2-4gpm where many of you are 15-20gpm, he's experimenting

If your losing 30 degrees from the stove to the hx like someone said, I'm willing to bet your thermopex is soaked. 

[fireboss]

iam sorry iam loosing 30 across the EX .  I dont loose hardly  anything from the wb  its only 14 feet away from house well 28 if you count there and back.  my house is 3000 sq . with new replace ment windows this summer. most of my house is very warm execpt my liveing room i cant get it past 65 -68 with the thermastat set at 75 the cirulater pump running all the time witch in turn cooks us out of the room that gets the heat first feels like iam chaseing a ghost